Magnetic pickup and tone modification circuit for stringed musical instrument

Abstract

A magnetic pickup assembly for a stringed instrument comprises a base plate and four ferrous rails or polepiece arrays, three magnets arranged between the four rails/poles, and four pickup coils. Two sets of two rails/poles are disposed on the base plate and include an inner set and an outer set. Each rail/polepiece array has a coincident coil. The three permanent magnets are specifically provisioned and attached to the base plate. The two humbucking outputs of the pickup are connected externally in a series configuration. A passive RC network is connected to the two coil pairs in series. By provision of component values of the RC network, output frequency response to string vibrations may be controlled over a wide range. The complete design provides a variable frequency-selective string aperture feature which assists in obtaining pleasing tonality over the range of adjustment. Alternate embodiments may use active electronic circuitry.

1 . An electronic pickup assembly for a stringed instrument, the electronic pickup assembly comprising:
 a base plate having first and second sides;   an inner pair of first rails disposed adjacent to one another in the base plate, each of the first rails having a first coil wound thereabout on the first side of the base plate, the first coils having a first inductance and being configured to provide a first independent output;   an outer pair of second rails disposed in the base plate, each of the second rails disposed adjacent to one of the first rails of the inner pair, each of the second rails having a second coil wound thereabout on the first side of the base plate, the second coils having a second inductance and being configured to provide a second independent output, the first inductance of the first coils being less than the second inductance of the second coils;   a first permanent magnet disposed on the second side of the base plate between a first set of the first and second rails adjacent to one another, the first permanent magnet having a first magnetic orientation transverse to the respective rails;   a second permanent magnet disposed on the second side of the base plate between a second set of the first and second rails adjacent to one another, the second permanent magnet having the first magnetic orientation transverse to the respective rails; and   an intermediate permanent magnet disposed on the second side of the base plate between the first rails adjacent to one another, the intermediate permanent magnet having a second magnetic orientation opposite to the first magnetic orientation.   
     
     
         2 . The electronic pickup assembly of  claim 1 , wherein the first coils are electrically connected in parallel; wherein the second coils are electrically connected in series; and wherein the first coils have a first set of coil turns being approximately equivalent to a second set of coil turns for the second coils, whereby the first inductance of the first coils is less than the second inductance of the second coils. 
     
     
         3 . The electronic pickup assembly of  claim 1 , wherein the first coils and the second coils are electrically connected in series; and wherein the first coils have a first set of coil turns being approximately less than a second set of coil turns for the second coils, whereby the first inductance in terms of the coil turns for the first coils is less than the second inductance in terms of the coil turns for the second coils. 
     
     
         4 . The electronic pickup assembly of  claim 1 , wherein one of:
 each of the first and second rails have an equivalent spacing from one another; and   the first rails of the inner pair have a first spacing, each of the second rails of the outer pair having a second spacing relative to the respective first rail adjacent thereto, the first spacing being different from the second spacing.   
     
     
         5 . The electronic pickup assembly of  claim 1 , wherein the base plate has a front edge and a back edge opposed to one another to which the first and second rails are arranged parallel; and wherein:
 the first magnetic orientation has a North pole toward the front edge and a South pole toward the back edge, and the second magnetic orientation has a South pole toward the front edge and a North pole toward the back edge; or   the first magnetic orientation has a South pole toward the front edge and a North pole toward the back edge, and the second magnetic orientation has a North pole toward the front edge and a South pole toward the back edge.   
     
     
         6 . The electronic pickup assembly of  claim 1 , further comprising control circuitry in electrical communication with the first and second independent outputs. 
     
     
         7 . The electronic pickup assembly of  claim 6 , wherein the control circuitry comprises a first-order Resistor-Capacitor (RC) network comprising:
 a junction in electrical communication with (i) one of two ends of the first independent output for the first coils electrically connected in parallel, and (ii) one of two ends of the second independent output for the second coils electrically connected in series;   a variable resistive component in electrical communication with the junction and being configured to provide a variable resistance; and   a first capacitor in electrical communication between the variable resistance and a ground of the control circuitry.   
     
     
         8 . The electronic pickup assembly of  claim 7 , wherein the other end of the second independent outlet is in electrical communication with the ground of the control circuitry; and wherein the control circuitry comprises:
 a second capacitor connected to the other end of the first independent output for the first coils; and   a second variable resistor having a resistive element and a variable output, the resistive element connected between the second capacitor and the ground, the variable output being configured to connect to an output of the control circuitry.   
     
     
         9 . The electronic pickup assembly of  claim 6 , wherein the control circuitry comprises:
 a junction in electrical communication with (i) one of two ends of the first independent output for the first coils electrically connected in parallel, and (ii) one of two ends of the second independent output for the second coils electrically connected in series;   a first variable resistor having first and second terminals of a resistive element and having a third terminal in variable electrical contact relative to the resistive element, the first terminal in electrical communication with the junction, the second terminal in electrical communication with the other end of the first independent output; and   a first capacitor in electrical communication between the third terminal of the first variable resistor and a ground of the control circuitry.   
     
     
         10 . The electronic pickup assembly of  claim 9 , comprising a resistor and a second capacitor connected in series between the second terminal and the other end of the first independent output. 
     
     
         11 . The electronic pickup assembly of  claim 9 , comprising a resistor connected in series between the third terminal and the first capacitor. 
     
     
         12 . The electronic pickup assembly of  claim 6 , wherein the control circuitry comprises:
 a junction in electrical communication with (i) one of two ends of the first independent output for the first coils electrically connected in parallel, and (ii) one of two ends of the second independent output for the second coils electrically connected in series;   a first capacitor in electrical communication with a ground of the control circuitry; and   a selective switch and at least one resistor in electrical communication between the junction and the first capacitor, the selective switch being configured to select a variable resistance.   
     
     
         13 . The electronic pickup assembly of  claim 12 , wherein the selective switch comprises:
 a first terminal in electrical communication with the junction, the junction connected to a first of the at least one resistor in electrical communication with the other end of the first independent output;   a second terminal connected between the first resistor and the other end of the first independent output; and   a pole in electrical communication with the first capacitor and configured to selectively switch between the first and second terminals.   
     
     
         14 . The electronic pickup assembly of  claim 13 , comprising a second resistor connected in series between the pole and the first capacitor. 
     
     
         15 . The electronic pickup assembly of  claim 12 , comprising a second capacitor connected in series between the selective switch and the other end of the first independent output. 
     
     
         16 . The electronic pickup assembly of  claim 6 , wherein the control circuitry comprises:
 a junction in electrical communication with (i) one of two ends of the first independent output for the first coils electrically connected in parallel, and (ii) one of two ends of the second independent output for the second coils electrically connected in series;   a first active buffer circuit having an input and an output, the input in electrical communication with the junction;   a parallel resistor-capacitor circuit in electrical communication with the input; and   a first variable resistor having first and second terminals of a resistive element and having a third terminal in variable electrical contact relative to the resistive element, the first terminal in electrical communication with the output, the second terminal in electrical communication with a ground of the control circuitry, the third terminal in electrical communication with the parallel resistor-capacitor circuit.   
     
     
         17 . The electronic pickup assembly of  claim 6 , wherein the control circuitry comprises:
 a junction in electrical communication with (i) one of two ends of the first independent output for the first coils electrically connected in parallel, and (ii) one of two ends of the second independent output for the second coils electrically connected in series;   a first active buffer circuit having a first input and a first output, the first input in electrical communication with the junction;   a first parallel resistor-capacitor circuit in electrical communication with the first input;   a first variable resistor having first and second terminals of a resistive element and having a third terminal in variable electrical contact relative to the resistive element, the first terminal in electrical communication with the first output, the second terminal in electrical communication with a ground of the control circuitry, the third terminal in electrical communication with the first parallel resistor-capacitor circuit;   a second active buffer circuit having a second input and a second output, the second input in electrical communication with the other end of the first independent output;   a second parallel resistor-capacitor circuit in electrical communication with the second input; and   a second variable resistor having first and second terminals of a resistive element and having a third terminal in variable electrical contact relative to the resistive element, the first terminal in electrical communication with the second output, the second terminal in electrical communication with the ground, the third terminal in electrical communication with the second parallel resistor-capacitor circuit.   
     
     
         18 . The electronic pickup assembly of  claim 1 , wherein each of the first and second rails share geometric and ferrous characteristics; and wherein each of the first, second, and intermediate permanent magnets share geometric and magnetic characteristics. 
     
     
         19 . The electronic pickup assembly of  claim 1 , wherein the first rails have a first magnetic field strength that is approximately twice a second magnetic field strength of the second rails. 
     
     
         20 . A stringed instrument, comprising an electronic pickup assembly according to  claim 1 .